In offshore activity, there is frequently a need to transfer liquid from a reservoir ship to a more mobile tanker for the carriage of the liquid to an onshore site. In oil production for example, oil pumped from a subsea well is normally delivered to such a floating reservoir from which tankers are loaded. Heretofore, the connection between the reservoir and the tanker has been accomplished by dragging the end of a hose from the reservoir directly to a coupling or union on the tanker deck. During part of its journey, the end of the hose will usually be freely suspended over the surface of the water, and particularly in adverse weather conditions, the operation can be extremely hazardous.
In accordance with the present invention, the movement of an object to a target is carried out substantially at or below the water surface. This is accomplished by the positioning of a target in the form of a cradle mounted substantially at or below the surface level of the water, and guiding the object into the cradle. The object is then secured in the cradle for further action as appropriate. Normally, the object will be drawn into the cradle by means of a line attached at one end to the object and at the other end to a winching mechanism. The line will pass through the cradle between guides disposed thereon specifically to locate the object as it is received therein, and in this way a positive location or docking of the object is achieved. However, for some applications of the invention the object may be free in the water, and have its own motive power and guidance mechanism directed towards and into the cradle. The cradle itself might have means for transmitting a homing signal to the object for this purpose.
As noted above, in order to receive the object, the target, which may conveniently be a cradle, as has been already stated, is disposed substantially at or below sea level. For some applications, the cradle may be fixed on its supporting body in a sealed compartment with doors openable to the sea to provide access for the incoming object. In one alternative, the cradle may be mounted on a track which is extendable from the compartment into the water so that the cradle can be moved to a position external to the supporting body to receive the object, and then retrieved with the object into the compartment. The track may be formed on a moveable frame for this purpose. It is of course also possible to have the cradle mounted externally of the body.
In this variation the cradle is movable on a track between two positions and has the track extending from a receiving position substantially at or below sea level, to another position above sea level, for example the deck of a ship. The track may be mounted directly in the side of the body or ship, or on a framework attached thereto. Such a framework may itself be moveable between an operative position on the side of the body and a storage position when it is not in use.
Where the invention is used with a line for drawing the object into the cradle, the line (in fact a pilot or messenger line) is dispatched from the receiver body or ship to the sender body for attachment to for example, the end of a hose. If the line is not already passing into and through the cradle to a winch, it is so threaded or attached to a draw line which is already in place, and the winch then activated to draw the hose end from the sender body into the cradle. If the hose end is initially above sea level, then it first falls into the sea but is then drawn substantially horizontally at or below sea level to the cradle. Normally, the buoyancy of the hose, and the hose end in particular, will be such that it is maintained at or just below the surface level of the water. In some cases, the hose end may be supported from surface buoys to ensure that the hose end does not sink, and thus impose excessive demands on the winch mechanism. By substantially establishing the path of the hose end in this way, the orientation of the cradle may be substantially fixed, and guides thereon adapted to effect the necessary alignment at final approach. It will be appreciated that the hose end supported at or just below the water surface, even in rough seas, is much less subject to unpredictable movement than it would be if freely suspended above the surface, either from a floating vessel or even from a stationary structure. Even so, some flexibility in the guides in the cradle is desirable and they could be resiliently mounted. Guides within the cradle also define a convergent entrance to the cradle. Guides external to the cradle may also be used to effect initial entry.
When the object such as a hose end is received in a cradle provision will be made for securing it therein either at a fixed orientation or, and particularly if the cradle is then to be moved, in a manner which permits the object to pivot. To this end, the cradle may be particularly adapted to receive objects with trunnions thereon, and be provided with guides in the form of slots for receiving the trunnions. Upon the object being fully received in the cradle, claws may close around the trunnions which permit pivotable movement of the object about the axis of the trunnions. Thus, where the cradle is mounted externally of the receiving body and adapted to be raised above sea level the object is suspended on its trunnions which enable it to pivot freely until the cradle reaches its onboard position.
As described above, the invention is particularly useful in the offshore industry where connections must be made between floating vessels for the transfer of liquids or gases therebetween. Such fluids include not only hydrocarbon fuels, but also water, drill mud and other substances which are capable of flowing as required. Where a connection is to be made to an underwater vessel such as a submarine, air and fresh water can be transferred in this way, and waste matter can be removed. Connections made according to the invention can also be used to transmit data and information along a cable or through a hose. Where the object received in the cradle is otherwise free in the body of water, it may be used as a transfer vehicle for solid matter, materials and equipment that cannot be moved along a duct or hose.
The cradles used in connection or transfer systems of the invention may take the form of tubes oriented substantially horizontally to receive the object which may conveniently be a hose end. A similar system to that used to connect multi-bore hoses to a well head on the sea bed can be adopted. Torpedo tubes can also be adapted to receive objects in systems embodying the invention, either drawn into the tube by a line or directed thereto by other means.
Where the invention is used to connect a hose or other conduits, once the hose end is safely received in the cradle, it can be coupled to a union of the receiving body using known coupling techniques, for example of the type used in the oil industry. Suitable transfer hoses are also available, although some adaptation may be necessary to connect a draw line to the end thereof and provide for safe guidance into the cradle. Conveniently, systems according to the invention may use a separate head unit which couples to the hose end using the fittings already available on the hose end, the head unit having been specially adapted to a particular cradle design. In this variant, once the head and the hose end are both safely received in the cradle, the head can be removed and the hose end coupled to a union on the receiving body in known manner.
Some embodiments of the invention will now be described by way of example and with reference to the accompanying schematic drawings wherein: